The invention relates to an electrical cable assembly, and, more particularly to a cable assembly for connecting a test circuit to a measuring instrument such as a logic analyzer or like instrument which analyzes timing signals from the test circuit.
A logic analyzer is typically used to display several lines of information related to the logic state of a circuit, and/or the point in time when detectable events occur within the circuit. The more precisely the logic analyzer can determine the exact point that the events occur, the more accurately the technician can evaluate the performance of the circuit.
A prior art logic analyzer cable is illustrated in FIG. 1 of U.S. Pat. No. 4,777,326 having a pod containing a resistor-capacitor attenuation circuit for each probe near the probe tip which is connected to a test circuit. A twisted pair cable attaches the pod to the measuring instrument, logic analyzer and the like, while a single wire connects the pod to the probe tip. The twisted pair cable is said to provide some shielding and crosstalk reduction, but that crosstalk is developed in the probe lead and additional shielding is still desired. The location of resistor-capacitor networks in the pod and not at the probe tips, is said to cause the probes to have a higher input capacitance. The resonant circuit formed by the single wire inductance and capacitance is said to limit the bandwidth of the probes.
U.S. Pat. No. 4,777,326 uses a resistive wire in a flat woven cable instead of a lump resistor in a network. The resistive wires for signals are said to alternate with lossless wires for ground to form a lossy transmission line. The cable is said to provide an effective bandwidth, and accurate signal duplication. The resistive wire is woven with conductive ground wires along each side for shielding.
It is known in the art to provide a woven resistive wire cable as described above which is terminated with conventional pin/socket connectors and to provide an interface shroud which fits over the connector at the probe end into which the probe leads are inserted and interlocked to mate with predetermined resistive wires to transmit test signals to the logic analyzer. U.S. Pat. Nos. 4,822,303; 4,433,888; and 4,008,941 show other typical cable assemblies having interlocking cable end parts for adapting various cable connectors and lead tips together.
Accordingly, an object of the invention is to provide a cable assembly and method for a logic analyzer which transmits high frequency logic signals from a logic circuit to a logic analyzer in an accurate manner for analysis over a wide bandwidth.
Another object of the invention is to provide a cable assembly for a logic analyzer and the like measuring instruments for transmitting high frequency signals from a test circuit with high fidelity over a wide bandwidth for analyzing a broad frequency range.
Another object of the present invention is to provide a cable assembly for a logic analyzer and the like for transmitting high frequency logic signals in which probe leads connected to the logic circuit may be easily connected and disconnected in the cable assembly in a reliable manner.
Another object of the present invention is to provide an electrical cable assembly for a signal measuring instrument which has a low input capacitance and high input resistance for broad bandwidth and high fidelity signal transmission.
Another object of the invention is to provide a cable assembly for a logic analyzer and the like for transmitting high frequency logic signals from a logic circuit to a logic analyzer wherein a conventional flat woven controlled impedance cable is utilized with resistor capacitor networks at each end to provide a wide bandwidth over which frequency signals may be transmitted and analyzed. This cable may be symmetrical or asymmetrical in construction.